The present invention relates generally to rotatable dynamoelectric machines, and, more particularly, to rotatable assemblies usable therein, and to methods for making the same.
Shafts of rotary dynamoelectric machines, such as fractional horsepower electric motors of both ball and sleeve bearing types, often are machined from shaft stock that initially is of a relatively large diameter. Extensive machining of large diameter shaft stock often has been required, even though one or more external shaft extensions are required to be of a small diameter. In some cases, large diameter stock is used so that intermediate diameter seats, and large diameter shoulders may be provided thereon for ball bearings. Moreover, in the case of shafts designed to accommodate ball bearings, a groove may be required adjacent the ball bearing seat to provide clearance for the inner race of the bearing.
Some sleeve bearing motors are provided with straight shafts, i.e., shoulders, steps, etc. are not normally provided. However, for other sleeve bearing motors, it has sometimes been necessary to provide enlarged shafts in order to increase the stiffness thereof, and machine the shaft extensions to a smaller, acceptable size. This usually is done in order to avoid vibration and noise problems when either the horsepower of a motor or the distance between bearings is increased.
Although the above problems may be encountered with different motors having different diameter shaft extensions, the problem as it pertains to motors having one-half inch (12.7mm) diameter shaft extensions will now be set forth in more detail.
For some ball bearing motors with a one-half inch diameter shaft extension, it has been necessary to machine the shaft from three-quarter inch (19mm) diameter stock. In these cases, multiple machining operations have been performed on each end of the shaft to provide a central shaft portion that remained three-quarter inches (19mm) in diameter, machined seats for a ball bearing [e.g., for a ball bearing with an inner race diameter of about .590 inch (15mm)]; and one-half inch (12.7mm) shaft extensions.
On the other hand, for some sleeve bearing type motors that required a nominal one-half inch (12.7mm) shaft extension, one-half inch diameter ends have been machined on a five-eights inch (15.9mm) diameter shaft to provide bearing journals and one or more shaft extensions of the desired one-half inch (12.7mm) size. Five-eights inch (15.9mm) diameter shaft material has been used so that the unsupported length of the shaft between the bearings would be stiffer and have less tendency to bend or whip during operation and thus generate less noise (as compared to a one-half inch (12.7 mm) straight shaft). As will be understood, such noise is objectionable because it may be transmitted to the environment directly, or through the structural mechanisms that are interconnected with either the motor shaft or the motor shell. In other one-half inch (12.7mm) shaft, sleeve bearing motor applications, the axial length of the rotor, and unsupported shaft length have been sufficiently small that one-half inch (12.7mm) shaft material has been used with no particular problem.
In large volume production operations, the need to produce different shafts because of different rotor lengths or bearing types increases manufacturing costs not only due to extra material usage and machining operations; but also because of extra capital investment for machining equipment and because of the expense associated with maintaining different types of production equipment.
Still another expense associated with the use of differently sized shafts is more directly related to the manufacture of the rotor body. It should be recalled that squirrel cage rotors for induction motors are made up of laminations that have a centrally located bore for accommodating the shaft. All of the above specifically described motors typically would have rotors with a common outer diameter. However, laminations for each different motor would have a shaft receiving bore of one-half inch (12.7mm), five-eights inch (15.9mm), or three-quarters inch (19mm), depending on the diameter of the central portion of the shaft.
It should now be understood that it would be extremely desirable to provide new and improved rotor arrangements, and methods and apparatus for making the same, that can be utilized to overcome any one or more of the above mentioned problems.
Accordingly, it is a general object of the present invention to provide improved rotor arrangements and methods for use in making the same, as well as dynamoelectric machines including such rotor arrangements, so that the above-identified and other problems may be overcome.
It is a more specific object of the present invention to provide a new and improved rotor assembly whereby motors that require a given single diameter shaft extension may utilize straight shafts of a minimum diameter even for ball bearing or long rotor applications that have previously required stepped or otherwise machined shafts.
Still another object of the present invention is to provide new and improved methods for use in manufacturing rotors that may be used in either sleeve or ball bearing applications.
It is a more specific object of the present invention to provide a new and improved rotor assembly wherein accessory means, assembled on a straight shaft so as to form part of the rotor assembly, satisfy the previous need for stepped shafts.
It is yet another general object of the present invention to provide new and improved methods for assembling accessory means with substantially straight shafts.